Tolterodine, (+)-N,N-diisopropyl-3-(2-hydroxy-5-methylphenyl)-3-phenylpropyl-amine, has the following structural formula (I)

Tolterodine is an anti-cholinergic agent and is known to be particularly useful in the treatment of urinary incontinence. The preparation of tolterodine is described in U.S. Pat. No. 5,382,600, where the following reaction scheme is followed.

Deprotection by removal of hydroxy protecting groups is achieved according to U.S. Pat. No. 5,382,600 by treatment with hydrobromic acid, borontribromide or by catalytic hydrogenation. In the case where deprotection is carried out in the presence of pyridine hydrochloride, such deprotection is carried out at high temperature (greater than 200° C.) and in the absence of a solvent. The reaction mass obtained is highly viscous and requires quenching to about 80-90° C. before the addition of water. Using such techniques, it has been found that at 100° C., a hard mass which cannot be stirred is obtained and which subsequently cannot be quenched.
A further problem associated with prior art preparation techniques is that dimeric impurities are generally associated with tolterodine tartate prepared thereby, typically at a level of approximately 0.15-2%. Typical impurities can be 2-(3-{[3-(2-hydroxy,5-methyl-phenyl)-3-phenyl-propyl]-isopropyl-amino}-1-phenyl-propyl)-4-methyl-phenol, and/or (3-{2-[2-(3-diisopropylamino-1-phenyl-propyl)-4-methyl-phenoxymetoxy]-5-methyl-phenyl}-3-phenyl-propyl)-diisopropyl-amine, having the following structural formulae

There is a need, therefore, for the provision of improved processes of preparing tolterodine, whereby the above problems encountered by employing prior art techniques can be alleviated and a product with improved purity can be obtained. This is now achieved by the present invention.